There are a number of medical conditions for which an effective therapy is driving current through a section of the tissue of a patient. Often the current is driven between electrodes of an electrode array implanted in the patient. Generally, the electrode array includes a non-conductive carrier on which typically two or more electrodes are disposed. Once the array is implanted, current is driven from at least one of the electrodes, through the adjacent tissue, to at least one of the other electrodes. The current flow through the tissue influences the tissue to accomplish a desired therapeutic result. For example, an electrode array positioned adjacent the heart may flow currents to stimulate the appropriate contraction and expansion of the heart muscles.
Current is also flowed from implanting electrode arrays into adjacent neural tissue to induce a desired neurological or physical effect. In one application, the current driven between the electrodes of an array placed on top of the dura in the vertebral column reduces the extent to which chronic pain signals are perceived by the brain. Alternatively, the array may be placed in a location where the current flow stimulates a feeling of satiation as part of an appetite suppression/weight management therapy. In another application, the current is flowed to tissue or nerves associated with the bladder or the anal sphincter to assist in control of incontinence. Electrodes may be implanted in a paralysis victim to provide muscle control and/or a sense of feeling.
The Applicants' Patent Application No. PCT/2009/33769, FOLDABLE, IMPLANTABLE ELECTRODE ARRAY ASSEMBLY AND TOOL FOR IMPLANTING SAME, published as WO 2009/111142, and IMPLANTABLE ELECTRODE ARRAY ASSEMBLY INCLUDING A CARRIER FOR SUPPORTING THE ELECTRODES AND CONTROL MODULES FOR REGULATING OPERATION OF THE ELECTRODES EMBEDDED IN THE CARRIER, AND METHOD OF MAKING SAME, filed 5 Aug. 2009 the contents of which are published as US Pat. Pub. No. 2011/0034977 A1, the contents of both of which are explicitly incorporated herein by reference, each describe an electrode array that includes a carrier on which plural electrodes are arranged in a row by column matrix. An advantage of this type of array is that it allows current to be flowed between numerous different combinations of electrodes. Depending on which electrodes are connected to associated current sources and sinks, this array can be operated so that there are two or more current flows occurring simultaneously between different sets of electrodes. Once this assembly is deployed, the practitioner can initially drive current between different combinations of electrodes. Current therefore flows through different sections of tissue. This allows the practitioner to determine between which electrodes, through which tissue, the current flow offers the greatest benefit and/or tolerable side effects. Once the optimal current flow path between the electrodes is determined, the array and its associated power supply are set to operate in this state.
In comparison to other electrode arrays with lesser numbers of electrodes, the above-described array makes it possible to flow current through more sections of tissue and to selectively focus/diffuse the current flow. In contrast to an electrode array with a smaller number of electrodes, use of the above-described array increases the likelihood that the current flow can be set to provide desired therapeutic effects, with tolerable side effects. Thus, this electrode array increases the likelihood that the flowing of current through the tissue of a patient can serve as effective therapy for certain medical conditions.
There are, however, limits to which the extent that a single electrode array can function as a useful therapeutic medical device. In particular, there are many situations where an individual may benefit by having current simultaneously flowed through different spaced tissue that are spaced apart 5 cm or more. For example, an individual may be suffering from the sensation of chronic pain in both the lower leg and upper arm. Presently, this medical condition would be treated by implanting into the a single implantable pulse generator and two spaced apart percutaneously implanted octrode (1×8) arrays, One octrode array would typically placed against the spine at level T8-T10 (lower leg). The second octrode array is placed against the spine at level C5-T1 (arm). At best, each octrode array is limited in the size and number of sections of tissue through which it can flow current. This means the ability of the array itself to provide pain relief is limited.
As an alternative, one could potentially place a single electrode against the upper extremity to attempt to treat the pain peripherally. Unfortunately, this may not provide satisfactory relief. One reason that, for the array electrodes to flow current through the tissues that would result in the desired therapy, the array would most likely have to extend over several internal joints. The repetitive stress and motion the array would undergo in this placement process would expose the array to a significant risk of prior to deployment, fracture. Also it may be difficult to place the array using the presently available delivery tools.
To mask the transmission of these pain signals, it may be necessary to simultaneously flow current through sections of the spinal cord spaced apart 5 cm or more. Present manufacturing restraints make it difficult to provide a single electrode that can be deployed over these widely spaced apart sections of tissue. Medically it may be difficult to precisely position an array so the spaced apart sections of the array itself are positioned over the tissue through which the current flows will offer the desired therapeutic effect. Even when it is possible to both provide and position such an array, there may be reasons why such a device has minimal utility. For example, if the array shifts position, the electrodes may not cover a section of targeted tissue through which the current flow will provide a therapeutic effect.
Also, it should be appreciated that, when simultaneously sourcing current through separate sections of tissue, it may be desirable to do so using electrodes that have different physical structures. This may be necessary if, in the same patient, it is necessary to provide treatment for both chronic pain and the side effects of Parkinson's disease. For example, in the spinal cord it may be desirable to implant an array designed to extend both arcuately and longitudinally over a section of the spinal column. Simultaneously, a ring electrode may be implanted in the basil ganglia to provide omnidirectional stimulation in the treatment of Parkinson's side effects.
The present common practice is to connect each of these different arrays with its own implantable pulse generator (IPG). Each IDC applies the current directly to specific on-array electrodes.
Thus, the present practice is to, when implanting plural electrode arrays in a patient, often implant plural IPGs. Typically, to implant an IPG, an incision is made into the patient to create a subcutaneous pocket for holding the IPG. Implanting plural IPGs increases the surgical trauma to which a patient is exposed in order to obtain the benefit of the plural electrode arrays.
There have been proposals to implant into a patient a single control unit capable of powering and controlling the current output by multiple spaced apart electrode arrays. One proposal has been to have this single control unit wirelessly transmit signals to the electrode arrays implanted in various locations throughout the body. To date, this has proved technically difficult to execute. Another proposal would be to simply connect each electrode array to this common control unit by its own set of wires. This implant would make it necessary to string numerous wires through the body of the patient. These wires would extend from a single location, the control unit. As the individual in whom these devices are implanted moves, the tissue and organs internal to the person also moves. Over time, the movement of the tissue and organs surrounding the wires can displace the wires. The individual sets of wires could eventually start to cross each other. Once this happens, there is the possibility that the movement of one set of wires results in the displacement of a second set of wires. This movement of the second set of wires could cause these wires to disconnect from the array to which they are connected. Alternatively, the movement of the second set of wires can cause the like displacement of the attached array. The array movement can result in its electrodes shifting position so that they are no longer disposed against the tissue through which current flow offers therapeutic benefit. Should the array be repositioned to this extent, it no longer functions for the purpose for which it is implanted.